Disordered and/or delayed communication and language development constitute a defining characteristic of mental retardation. The proposed research is guided by a conceptualization of communication and language development that stresses the central role of the developmental cusp-an intersection in the interaction of behavior, skill, perception, or motivation, that is crucial to what should come next in development. Until the cusp is negotiated, development along that route may essentially stop;successful negotiation then permits a significant set of subsequent developments to occur. The cusps addressed in the present proposal are closely related to and representative of communication challenges of individuals with severe or profound mental retardation or at risk for severe mental retardation. Our recent research suggests that their communication impairments are at least partially amenable to intervention. Thus, we propose to further our understanding of these developmental cusps as we examine strategies for their negotiation. The cusps are conceptualized to lie on a continuum of communication development from pre-intentional to beginning symbolic communication. The cusps are contingency discrimination, triadic eye gaze, and symbolic communication using voice output communication aides (VOCA). Our strategies are built on nearly four decades of study. Specifically, we intend to show how children and adults with profound multiple impairments can learn to request assistance with adaptive switches (Project I: R. Saunders et al.);how triadic eye gaze for joint attention can be established in very young children with moderate or severe motor impairments (Project II: Olswang et al.);and how acquisition of symbolic communication using VOCA affects the development of successful communication exchanges (Project III: Brady et al.). All projects propose to identify participant variables that predict success in crossing the particular cusps they are studying. In addition, the relationship between the two earlier developing cusps studied by Projects I and II and later communication as studied by Project III will be investigated through both prospective and retrospective analyses.